mmc: core: Add cache control for eMMC4.5 device

This patch adds cache feature of eMMC4.5 Spec.
If device supports cache capability, host can utilize some specific
operations.

Signed-off-by: Seungwon Jeon <tgih.jun@samsung.com>
Signed-off-by: Jaehoon Chung <jh80.chung@samsung.com>
Signed-off-by: Chris Ball <cjb@laptop.org>
diff --git a/drivers/mmc/card/block.c b/drivers/mmc/card/block.c
index 3704727..c0cb225 100644
--- a/drivers/mmc/card/block.c
+++ b/drivers/mmc/card/block.c
@@ -851,16 +851,18 @@
 static int mmc_blk_issue_flush(struct mmc_queue *mq, struct request *req)
 {
 	struct mmc_blk_data *md = mq->data;
+	struct mmc_card *card = md->queue.card;
+	int ret = 0;
 
-	/*
-	 * No-op, only service this because we need REQ_FUA for reliable
-	 * writes.
-	 */
+	ret = mmc_flush_cache(card);
+	if (ret)
+		ret = -EIO;
+
 	spin_lock_irq(&md->lock);
-	__blk_end_request_all(req, 0);
+	__blk_end_request_all(req, ret);
 	spin_unlock_irq(&md->lock);
 
-	return 1;
+	return ret ? 0 : 1;
 }
 
 /*